1. Field of the Invention
Generally, the present disclosure relates to the field of integrated circuits, and, in particular, to embedded capacitors.
2. Description of the Related Art
Integrated circuits typically include a large number of circuit elements, which form an electric circuit. In addition to active devices such as, for example, field effect transistors and/or bipolar transistors, integrated circuits may include passive devices such as resistors, inductors and/or capacitors.
As integration density of semiconductor devices increases, the area occupied by individual devices continues to shrink. Notwithstanding this, a capacitor for storing data of, for instance, a dynamic random access memo (DRAM) is required to have a sufficient capacitance, irrespective of the decrease in the area occupied by the capacitor. In addition to so-called native capacitors, which make use of the native or “parasitic” inter-metal capacity between metal lines in integrated circuits, there are metal-insulator-metal (MIM) capacitors. Accordingly, a metal-insulator-metal (MIM) capacitor, in which a lower electrode and an upper electrode are formed of metal and separated by a layer of insulating material, is being used in many integrated circuit products. Metal-insulator-metal capacitors may be used in CMOS, BICMOS and bipolar integrated circuits. Typical applications of metal-insulator-metal capacitors include filter and analog capacitors, for example, in analog-to-digital converters or digital-to-analog converters, decoupling capacitors, radio frequency coupling and radio frequency bypass capacitors in radio frequency oscillators, resonator circuits, and matching networks. Additionally, MIM capacitors have been used extensively in semiconductor devices that perform analog-to-digital conversions and digital-to-analog conversions. Conversion between analog and digital signals requires that capacitors employed in such conversion be stable, i.e., the capacitance of the capacitors must be relatively stable over a range of applied voltages and temperatures. The capacitance of capacitors with polysilicon electrodes tends to be relatively unstable since the capacitor structures tend to vary with changes in temperature and applied voltage. Accordingly, capacitors with polysilicon electrodes are typically not used for such conversion applications Metal-insulator-metal capacitors may be provided in additional interconnect levels, which are provided in addition to interconnect levels wherein electrically conductive lines connecting active circuit elements of integrated circuits, such as, for example, transistors, are provided.
Key attributes of metal-insulator-metal capacitors may include a relatively high linearity over relatively broad voltage ranges, a relatively low series resistance, relatively good matching properties, relatively small temperature coefficients, relatively low leakage currents, a relatively high breakdown voltage and a sufficient dielectric reliability.
Techniques for forming metal-insulator-metal capacitors may include a deposition of a metal-insulator-metal stack on a planarized surface of a semiconductor structure and a patterning of the metal-insulator-metal stack. The metal-insulator-metal stack may include a bottom electrode layer, a dielectric layer and a top electrode layer. The metal-insulator-metal stack may be patterned by means of a photolithography process. However, the absorption and/or reflection of light by the metal-insulator-metal stack is largely depending on the materials used and the thicknesses of the layers in the metal-insulator-metal stack. Thus, there are limited material combinations that enable optical alignment through the metal-insulator-metal stack.
In forming the upper and lower metal electrodes of a MIM capacitor, an etching process is typically performed to pattern a metal layer. However, as the integration density of semiconductor devices continues to increase, it is becoming more difficult to etch such metal layers. In particular, copper, which has good electromigration resistance and a desirable low resistivity, may be difficult to etch. Accordingly, various methods for forming the upper and lower metal electrodes through a damascene process, that is, a process which does not involve etching a metal layer, have been proposed. A copper damascene process generally includes forming a trench for a copper structure in an insulation layer, forming a sufficient amount of copper to overfill the trench and removing the excess copper from the substrate, thereby leaving the cooper structure in the trench. However, the damascene process used in forming copper-based capacitors and conductive lines and vias is time-consuming and expensive, and includes many steps, where chances for creating undesirable defects always exist.
Moreover, capacitors of the art suffer from the following problems. Vertical natural capacitors and finger metal-oxide-metal capacitors show insufficient capacitance due to low values of the dielectric constants of the used ultra-low-k dielectrics that, in principle, require large areas to provide significant capacitance anyway. The voltage of lateral capacitor, on the other hand, is limited, in principle, by the operation reliability of the employed ultra-low-k dielectrics.
The present disclosure provides enhanced capacitor structures and manufacturing processes for the same wherein the above-mentioned issues may be properly addressed and the mentioned problems of the art may be overcome or at least alleviated.